1. Field of the Invention
The present disclosure is related panel boards for electric power distribution systems. More particularly, the present disclosure is related to replacement panel boards and methods for selecting replacement installed panel boards.
2. Description of Prior Art
Electrical systems in residential, commercial, and industrial applications usually include a panel board for receiving incoming lines of a distribution system delivering electrical power from a utility source or generator. The power is routed through the panel board via one or more current interrupters, such as circuit breakers, to numerous branch circuits in the system.
Over current protection is typically provided for the branch circuits in older panel boards by fuses and more recently, by circuit breakers. Additional protection, such as surge protection, ground fault protection, and arc fault protection is also provided in some panel boards.
The panel board includes a box-like enclosure with an open front and is usually formed from sheet metal. Typically, a main circuit breaker or main lugs connected in series with separate single or multi-pole circuit breakers for the branch circuits are collectively housed within the panel board enclosure. Each branch circuit breaker distributes the power from a distribution bus to a designated branch, where the branch supplies one or more loads with the power. The circuit breakers are configured to interrupt the power to the designated branch if certain electrical conditions, such as the instantaneous current for example, in that branch reach a predetermined level.
A structure commonly referred to as an interior assembly is mounted within the enclosure. The interior assembly mechanically supports the circuit breakers, which are mounted in selected positions, and electrically connects them to the distribution bus. The interior assembly typically includes a pair of line buses secured by a supporting insulator. The fuses or circuit breakers connect a conductor for each branch to one of the line buses, or to both buses in the case of a two-pole breaker. The interior assembly also includes one or more neutral terminal blocks to which the branch circuit neutral conductors are connected. In some cases, such as for ground fault circuit breakers, a ground terminal block is provided.
The panel board enclosure must have a cover to ensure there are no direct uncovered openings from the interior of the enclosure. In the event of a short circuit for instance, any direct opening would allow dangerous sparks and gases to exit the enclosure, thereby creating a hazard. Additionally, even in the absence of an electrical fault, uncovered openings create an additional risk of unsafe unintentional access to live electrical parts.
A cover, usually defining a window-like opening, is mounted over the open front of the enclosure and secured to the enclosure with screws. A single dead front is mounted over the window-like opening of the cover to provide access to circuit breakers installed therein while blocking any direct uncovered openings proximate to the circuit breakers. The dead front is typically provided with a plurality of generally rectangular removable plates or “knock-outs”. As circuit breakers are installed by an electrician into the panel board, the knock-out plates are removed to form generally rectangular apertures on the dead front corresponding to the shape and location of the installed circuit breakers Additionally, a hinged door is often attached to the cover to secure the enclosure providing lockable access to the dead front and the installed breakers that protrude through the apertures in the dead front.
Local electrical codes and industry standards, such as Standard UL 50 for Enclosures and Standard UL 67 for Panel Boards, detail specific requirements related to the fastening of the panel board cover to the enclosure. For example, Standard UL 50 requires that there be at least one cover fastenings located not more than 6 in. (152 mm) from each of the four corners of the enclosure, and the spacing between adjacent cover fastenings must be not more than 24 in. (610 mm).
An illustration of a conventional panel board is shown in exploded view in FIG. 1. A typical panel board 11 consists of an enclosure 21 having a rear wall 41, and four walls 51, 61, 71, 81. Mounted within the enclosure is a structure typically referred to as a panel board interior 91, for mounting at least one circuit breaker 111 with a face 171 with an operating handle 151 extending therefrom. Additionally, the interior 91 comprises at least one distribution bus 121 for electrically connecting the at least one circuit breaker 111 thereto. Also included, within the enclosure 21 at least one of a neutral bus 131 and a ground bus 141 are also mounted as part of the interior 91.
The conventional panel board 11 additionally consists of a cover assembly 161. Often the cover assembly 161 consists of a cover plate 301 defining a window like opening 311, and a single dead front plate 331. The single dead front plate 331 is positioned within window-like opening 311 of cover plate 301 and secured using screws to tabs 361, 371 on cover plate 301. The dead front plate 331 is configured to provide one or more apertures 341 that register with each installed circuit breaker face 171 and operating handle 151 and is configured to allow access thereto, while preventing finger access to electrically live parts. Removable plates 441, commonly referred to as knock-outs or twist-outs, are provided integral to single dead front plate 331 to enable customizing the quantity and location of the one or more apertures 341 as needed on dead front plate 331.
Typically, the cover assembly 161 is secured using screws (not shown) to flanges, 181, 191, 201, 211 formed at right angles to the walls 51, 61, 71, 81 of the enclosure 21. In some cases, the cover assembly is secured to brackets (not shown) mounted with the enclosure 21. A hinged door 221 with latch 241 attaches to the cover plate 301 to cover the dead front plate 331 when in the closed position. In some cases, springs (not shown) positioned between dead front plate 33 land the cover 301 are used to provide depth adjustment of the height of dead front plate height 331 within the enclosure 21 and prevent finger access to electrically live parts within the enclosure. In other instances, an adjustable riser (not shown) may be used instead to adjust the height of the panel board interior 91 outward toward the first dead front plate 331.
In some cases, a support structure (not shown), such as a mounting plate for example, may be used to mount the interior 91 at the proper depth within the enclosure 21 and with the required spacing to the enclosure walls 51, 61, 71, 81. The support structure (not shown) is preferably mounted using screws (not shown) to the rear wall 41 of the enclosure 21. The support structure (not shown) is located and configured to position the panel board interior 91, inclusive of any circuit breaker 111 mounted thereon, to maintain at least predetermined minimum spacing to each of the four sidewalls 51, 61, 71, 81. The predetermined spacing dimensions are specified by local electrical codes or industry standards, such as Standard UL 67 for example, and are intended to allow sufficient room for locating and orienting branch circuit cables (not shown) as well as to provide at least minimum distances between electrically live parts and grounded parts, such as the enclosure 21 for example.
The panel board enclosure 21 is usually fixedly mounted on a wall (not shown) or is recessed into a wall (not shown) so that the cover assembly 161 is substantially flush with the wall surface (not shown).
Most conventional panel board enclosures have a generally standard width of approximately 10-14 in. (25.4-35.6 cm), enabling ready installation between studs on walls having standard construction stud spacing of about 16 in. (40.6 cm) on center. Panel board enclosures are known to vary greatly in the height depending on the manufacturer and the number of branch circuits supported as well as other factors.
There is often a need to update or replace older panel boards that have been previously installed in the field, such as where an updated panel board with circuit breakers is desired as a replacement for a fuse panel board, or for instance, where branch circuits need to be added. For cost and convenience reasons, such as for example where a panel board is flush mounted in a concrete wall, replacing the entire panel including the enclosure would require significant effort and cost, it is frequently preferable to replace or retrofit the installed panel board without removing or replacing the panel board enclosure.
Often the desired new replacement panel board interior is physically smaller than the prior panel board interior. For example, many older style 1 in. (25.4 cm) wide circuit breakers can be replaced by identically rated newer ½ in. (1.27) wide circuit breakers. Conversely, in many cases, additional branch circuit breakers may be desirable, requiring a somewhat larger panel board interior that still fits within the original enclosure.
The disparity in size between the original panel board interior and the retrofit panel board interior has required additional time and cost to ensure proper fit of the new interior in the previously installed enclosure, proper alignment of the new circuit breakers, and compliance with local and UL Standards. For example, retrofitting new interiors and circuit breakers into old enclosures has required careful measurements, customized new supports, and shimming of the replacement interior to properly adjust the depth of the new circuit breakers within the enclosure and properly register the new circuit breakers with the dead front openings, while maintaining all required UL spacing and clearances.
There is a need, therefore, for an improved retrofit panel board and method of selecting a panel board. It is desirable to have an improved panel board retrofit kit that is capable of Listing by Underwriters Laboratories, Inc. by ensuring that all requirements of Standard UL 50 and UL 67 are satisfied when properly installed, thus avoiding the need and cost for an in-field inspection after installation by an Underwriters Laboratories field inspector.
Accordingly, it has been determined by the inventors of the present disclosure that there is a continuing need for panel board retrofit kits and methods of selecting that overcome, alleviate, and/or mitigate one or more of the aforementioned and other disadvantages of prior art systems.